Temperature and humidity control for refrigerated display cases



TEMPERATURE AND HUMIDITY CONTROL FOR'REFRIGERA'IED DISPLAY GASES Sept. 2, 1952' M. W. STEELMAN Filed Oct. 2, 19.50

luvsm'on MELvm W. STEELMAN ATTORNEYS Patented Sept. 2, 1952 TEMPERATURE AND HUMIDITY CONTROL FOR REFRIGERATED DISPLAY GASES Melvin W. Steelman, Cobleskill, N. Y., assignor to Tyler Fixture Corporation, Niles, Mich., a corporation of Michigan 1 Application October 2, 1950, Serial No. 187,859

2 Claims.

The present invention relates to a temperature and humidity control apparatus, which in practice is used in connection with the maintenance of the air with which articles of food are surrounded in an open cabinet at a substantially unchanging condition, the temperature which effect such articles being controlled within preselected rather narrow limits, and the humidity of such air being likewise maintained substantially uniform or within a narrow range.

In open display cabinets which employ forced convection refrigerating systems, a certain inescapable amount of mixing of the refrigerated air entering the cabinet with air from the surrounding or outside atmosphere occurs. Such outside air, due to constantly changing atmospheric conditions, will carry greater or less amounts of vapor, causing an altering of the humidity of the air circulating through the system, and the outside air will have differing temperatures depending upon atmospheric conditions and, in order not to be detrimental to the merchandise displayed and sold, such air before coming to the merchandise should be lowered in temperature and its water vapor content controlled. Both temperature and humidity must be held within a close range to preserve the quality and appearance of many food articles, for example, cake icings and candy and especially chocolate coatings upon cakes or other similar articles of food.

My invention is directed to and has for its objects and purposes the provision of a refrigerating system which includes a conventional compressor, using the standard control means for starting and stopping, the starting occurring when the temperature of the air which is cooled or refrigerated reaches a predetermined higher degree and stopping it when such temperature is reduced to a predetermined lower degree. The usual evaporator coil is associated with the compressor but, additionally, another coil is used which serves as a source of heat for air which has been cooled and its moisture removed to a desired degree after it has passed through the evaporator coil and which, when it passes through the second or heating coil, has the temperature of such air raised before entering the display compartment in which the articles to be maintained in a cooled or refrigerated condition are located. Such heating or raising of the temperature of the air, which is at a. relatively low temperature when it passes from the evaporator or refrigerating coil, conditions the air thus passed to the display compartment for best maintaining the food articles not only in a cool or cold condition but not subjected to the moisture-which the delivered air would normally maintain or sustain. Such coils are of proper size and designed so as to maintainthe proper balance between the cooling and heating coils. The-heating coil is connected with the evaporator by a conduit which meters the passage of the refrigerant in proper amounts, to maintain a predetermined coil temperature of the evaporator It is further an object and purpose to associate with the condenser, the refrigerant being forced to such condenser, a fan for blowing'a current of air therethrough, so that the refrigerant has its temperature, raised by compressing, lowered to a greater or less degree in accordance with whether the fan is operating or not operating. The refrigerant fluid passes from the condenser direct to the heating coil, Electric control means are utilized for stopping the fan with the compressor continuing in operation, the stopping and starting of the fan being controlled by the temperature of the air as it entersthe food holding and display compartment. The compressor in its starting and stopping is controlled by the temperature of the refrigerated air leaving the evaporator or refrigerating coil before it passes through the heating coil. The usual temperature feeler bulbs for controlling thermostatic switches, one associated with the fan motor circuit and the other with the compressor motor circuit, are located, the one in the'air conduit at a point closely adjacent where the conditioned air enters the display compartment, and the other between the evaporator and heater coils.

One thermostat is set to stop the fan from blowing air through the condenser when the air entering the display compartment drops below a desired or too cold temperature. The condenser fan is started when the temperature of such ,air rises to a predetermined degree. The other thermostat is controlled in accordance with common practice in mechanical refrigeration, stopping and starting the compressor in accordance with the limits of temperature, high and low, which the refrigerated air has when it passes from the evaporator or refrigerating coils. Therefore, the major object and purpose of my invention is to provide a mechanism which willmaintain both temperature and humiditi in the cooled or refrigerated air which is supplied. to the'opentop display compartment, at preselected and predetermined best conditions'for the food articles which areto be affected :by said air, by novel, practical and useful structure, an understanding of which may be had from the following description, taken in connection with the accompanying drawing, in which,

The figure is a perspective view partly in section, diagrammatically illustrating the structure which embodies my invention.

In the structure shown in the drawing, a base I having a bottom and upwardly projecting sides and ends has, at the upper edges of said sides and ends of the base, a vertical double thickness wall 2 providing a compartment, in connection with a horizontal bottom 3 at approximately the same plane as the upper edges of the sides of the base, at each longitudinal side edge of which is an upwardly extending side member 4 at one side and 5 at the other, spaced from adjacent side walls 2. The air, at a lower temperature than the atmosphere, is carried at the outer side of the side 4 and over its upper edge, descending into the compartment and leaves at the opposite side over the upper edge of the side 5, there being longitudinal guide and deflector plate 6 over and spaced a short distance from the upper edges of the sides 4 and 5, one directing the incoming air downwardly and the other taking the outgoing air underneath it, as indicated by the arrows.

At the under side of the bottom 3 is a generally horizontal plate I generally parallel to the bottom 3, spaced a short distance below it for the major portion of the width of said bottom 3, but terminating adjacent one side as shown. The base within the vertical side and end walls thereof is chambered, as indicated at 8. An opening 9 is made in the member I so that outgoing air passing over the upper edge of the side 5 and downwardly through the passage between said side and the adjacent walls 2 comes into the space Ill between the bottom 3 and the member 1, goes through the opening 9 and through the chamber at 8, leaving at the opposite side and passing upwardly through the space [I between said opposite side 4 and the adjacent wall 2, thence over the upper edge of the side 4 for a downward direction into the compartment in which the merchandise, usually food products, is held upon and over the bottom 3. The upper side of the compartment is open and in direct communication with the air of the outside.

An electric motor driven fan I2 is located in the opening 9, the rotation of which impels the circulation of air in the directions indicated by the arrows and has been described. The motor of such fan is operating continuously when the case is in use, circuit wires I3 and I4 connecting to opposite-sides of the'motor and, in turn, leading to a suitable source of electric current.

The compressor I5 of a refrigerating system pumps or forces the fluid refrigerant used through an outlet pipe I6 to a condenser I1 which is of conventional structure. In an opening in a, vertiant afterit passes from the condenser.

cal side of the condenser a motor driven fan I8 is mounted for rotation. The motor of such fan has a wire I9 connected at one side thereof at one end, the other end of the wire I9 leading to a thermostatically controlled opening and closing switch 20. The other circuit wire 2I connected at one end at the opposite side of the fan motor is connected to one of the current supplying wires, such as the wire I4. A wire 22 connected at one end to the other current suplying wire I3 leads to a contact which the switch 20 electrically connects with when in closed position. 'When in such closed position the fan I8 is driven, forcing air through the condenser, thereby cooling the '4 fluid refrigerant which has had its temperature raised in its compression by the compressor.

In the passage I I for the incoming refrigerated air the control feeler bulb 23, associated with the thermostatic switch 20 is placed, having the usual connecting tube 24 leading therefrom to the thermostatic switch 29. When the temperature of the incoming air rises substantially to the predetermined or preselected highest temperature of the air which is wanted, switch 20 is closed and the fan I8 is driven to dispose of or eliminate heat which otherwise would be retained in the refriger- On the other hand, when the temperature of the incoming air to the food holding chamber lowers substantially to the lowest point of temperature wanted for the air, the feeler bulb 23 operates through the connection 24 to cause the switch 29 to open, whereupon the fan I8 is stopped in its rotation and the temperature of the refrigerant passing from the condenser I'I rises.

The electric motor driving the compressor has one of its electric circuit wires 25 associated therewith leading to and connecting with a second thermostatically controlled switch 26. The other circuit wire of the motor 21, like the wire 2!, connects with the circuit wire I4, while a wire 28 connects the other main circuit wire I3 with the closure contact for the switch 26. A feeler bulb 29, with the connecting'tube 30 connected and associated therewith, leads from said feeler to the thermostat which includes the switch 26 for opening and closing .the switch in accordance with the preselected maximum and minimum temperature to which the feeler 29 is subjected, closing the switch in order to cause the compressor to be operated when such temperature is at its highest preselected degree of temperature, andopening it to stopthe compressor when the temperature affecting the feeler 29 has reached the low, preselected temperature wanted.

In the chamber '8, immediately below the member I and substantially midway between the two opposite sides of thechamber, an evaporator or refrigerant expansion coil 3| is mounted, which may consist of a. plurality of connected tubes, usually finned, for rapid conduction of heat. From one end of this evaporator a suction conduit 32 leads to the inlet side of the compressor I5, so as to take the refrigerant when it has expanded and has become largely gaseous in character into the compressor for its condensation, in the main, to a liquid form.

A second tubular coil 33, is mounted at approximately the same level as the evaporator 3| between such evaporator and the outlet passage at II for the air supplied to the food chamber. It is of the finned, tubular well-known structure. The'fiuid refrigerant from the condenser I7 is carried through a pipe conduit 34 to the coil at-33 which, in the structure disclosed, is known as the heating coil. Aconducting or capillary tube 35 connects the outlet end of the heating coil at 33 with the inlet endof the evaporator coil at 3i. Such connectingtub-e is known as a metering tube, which permits the flow of a regulated or measured quantity ofthe refrigerant through it.

The air which leaves the food containing chamber, and which may have mixed therewith air from the atmosphere to some extent, and

' which mayand many times does carry more of which is low due to the absorption of heat when the refrigerant expands and becomes gaseous in the evaporator. The air passing through such cold coils of the evaporator will be dehydrated because lowered in temperature, and the moisture therein condensing upon the tubes and fins of the evaporator. Such air being too cold, or at a lower temperature than wanted in connection with the food products in the open food holding chamber above the bottom at 3, it is raised in temperature by passage through the heater at 33. In its dehydrated, higher temperature condition it is then impelled through the passage 12 to and over the upper edge of the inlet side 4 of the food containing chamber. Its moisture, which in varying amounts may have been introduced into the circulating air by the reception of outside air through the open top of the case, has been removed at the evaporator and its temperature, too low when it leaves the evaporator, has been raised to the desired degree before it comes to the food products which the case carries and displays.

The temperature of the heater coil 33 is increased when the fan I8 is not running. Under such conditions, with a continuation of the running of the compresser, heated refrigerant vapor is forced into the heating coil, whereupon latent heat of condensation of such vapor to liquid increases the warming process, and lifts or increases the temperature of the heating coil, thereby raising the temperature of the air which passes through such coil until the air inlet temperature in the passage I2 reaches the high range setting of the thermostat containing the switch 20, whereupon such switch 20 is closed and the fan I8 driven, or its running resumed. The fan then continues its running until, through a resultant lowering of the temperature in the heating coil, the temperature of the air in the inlet passage ll reaches the low range setting of the thermostat containing switch 20, whereupon the switch opens and fan l8 stops.

The thermostat containing the switch 26 located between the evaporator and heater is for control of the temperature of the air leaving the evaporator 3| starting and stopping the compressor in accordance with its range setting. The starting and stopping of a compressor is in the main, as to times of operation, independent of the times of starting and stopping the fan l8.

With the system and structure incorporating it as described, incoming air, dehydrated by its initial lowering of temperature by passage through the evaporator coils at 3|, comes into the food holding chamber at a higher temperature than the low temperature required for such moisture removal, by immediately passing through the heater coil at 33 upon its leaving the evaporator, which has done the work of moisture removal from the air. The temperature of the air to which the food products should be subjected is not a very low temperature and in general may be approximately 60 Farenheit (through subject to variation), which is higher than the temperature at which the evaporator can be operated for proper dehydrating or moisture'removal. Such relatively low temperature air leaving the evaporator coil at 3| is too low for best preservation of the food products in the open chamber of the case, and the temperature is raised without danger of addition of moisture to the air when it passes through the heating coil. Such temperature of the inlet air to the food containing chamber of the case is regulated within quite close limits.

It is to b understood that the invention is not to be limited to refrigerators having open compartments continuously exposed to the air, in which food products or the like are to be placed. The removal of moisture from air circulating in a closed refrigerator by passing over or through a low temperature evaporator coil, and the raising of the temperature of such dehydrated air after suchpassage, so that the air entering the food compartment is tempered and warmer than it would otherwise be, is desirable in many cases, one of which, as an example, would be where food products or the like from which water vapor escapes is placed in a closed refrigerator compartment, and the moisture added to the circulating air should be removed in whole or in part.

The structure described is very practical and useful and secures the desired results in an exceptionally satisfactory manner. The invention is defined in the appended claims and is to be considered comprehensive of all forms of structure coming within their scope.

I claim:

1. Means for controlling the temperature and humidity in an open top display case comprising means for circulating a current of air to pass under said case and across said case above its bottom, a cooling evaporator and a heating unit in said air current under the case in position to have air circulate first past the cooling evaporator and then past the heating unit, refrigerating mechanism for cooling the cooling evaporator, thermosensitive means located in the air current between the cooling evaporator and the heating unit for controlling operation of the refrigerating mechanism, and thermosensitive means in the air current beyond the heating unit in the direction of its flow for controlling operation of the heating unit.

2. The elements of claim 1 in which said refrigerating mechanism includes a refrigerant compressor, a condenser and a fan therefor, conducting means for the refrigerant from the compressor to the condenser, thence to the heating unit, thence to the cooling evaporator and thence to the compressor, said first thermosensitive means between the evaporator and the heating unit acting to control operation of the compressor and said second thermosensitive means in the air current beyond the heating unit acting to control operation of said condenser fan.

MELVIN W. STEELMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,837,798 Shipley Dec. 22, 1931 1,986,863 Terry Jan. 8, 1935 2,438,120 Freygang Mar. 23, 1948 2,494,480 MacMaster Jan. 10, 1950 2,515,842 Swinburne July 18, 1950 

